Automatic: Use Tools menu > Generate Local Resource File. This creates the App_LocalResources folder (if neccessary) and the RESX file and adds the meta:resourcekey attributes to the controls. Key string properties (Text, Caption, etc.) are externalized to the file via a Key.Property lookup.

Implicitly: Add the meta:resourcekey attribute to any control, and add the Key.Property entries in the RESX file(s) as needed.

Miscellaneous Text: Use the asp:Localize control with the meta:resourcekey attribute.